JP6885510B2 - Skimmer cone and inductively coupled plasma mass spectrometer - Google Patents

Description

The present invention relates to a skimmer cone having a hole formed at the top of a conical member used in a plasma mass spectrometer or the like, and an inductively coupled plasma mass spectrometer provided with such a skimmer cone.

One of the devices for analyzing elements contained in a sample is an inductively coupled plasma mass spectrometer (ICP-MS: Inductively Coupled Plasma Mass Spectrometer) (for example, Patent Document 1). The inductively coupled plasma mass spectrometer has the feature that it can analyze a wide range of elements from lithium to uranium (excluding some elements such as rare gases) at the ppt (parts per trillion = 1/1 trillion) level. It is used to quantify heavy metal elements contained in environmental samples such as seawater and river water, for example.

FIG. 1 shows the main configuration of the inductively coupled plasma mass spectrometer 100.
The inductively coupled plasma mass spectrometer 100 includes an ionization unit 110 that generates atomic ions from a sample by inductively coupled plasma, and a mass spectrometer 130 that separates and detects the generated ions by mass separation. The ionization unit 110 includes a plasma torch 112 arranged in an ionization chamber 111 having a substantially atmospheric pressure. The plasma torch 112 is composed of a sample tube for flowing a liquid sample atomized by nebulizer gas, a plasma gas tube formed on the outer periphery of the sample tube, and a cooling gas tube formed on the outer periphery of the plasma gas tube. There is. In the ionization unit 110, the liquid sample sprayed from the sample tube is atomically ionized by high-temperature plasma generated from a raw material gas such as argon gas supplied from the plasma gas tube.

The mass spectrometer 130 comprises a multi-stage differential exhaust system including a first vacuum chamber 141, a second vacuum chamber 142, and a third vacuum chamber 143 in which the degree of vacuum is gradually increased from the side of the plasma torch 112. The vacuum chamber 131 is provided. A sampling cone 144 is provided at the inlet of the first vacuum chamber 141. Further, a skimmer cone 145 is provided between the first vacuum chamber 141 and the second vacuum chamber 142. Inside the second vacuum chamber 142, an ion lens 146 for converging the flight trajectory of ions and a collision cell for removing interfering ions such as polyatomic ions by colliding with an inert gas such as helium gas. 147 are arranged. A quadrupole mass filter 148 (pre-rod and main rod) and a detector 149 are arranged in the third vacuum chamber 143. Atomic ions generated by the plasma torch 112 pass through the sampling cone 144 and the skimmer cone 145 to align the movement directions and form a small-diameter ion beam, and then mass-separate by a quadrupole mass filter 148. Is detected by the detector 149.

At the tip of the plasma torch 112, plasma having a high temperature of 6,000 to 10,000 K is emitted, and a part of the plasma travels along the outer peripheral surface of the sampling cone 144. Further, a part of the high temperature plasma irradiated to the sampling cone 144 passes through the hole formed at the top of the sampling cone 144, enters the first vacuum chamber 141, and travels on the outer peripheral surface of the skimmer cone 145. In this way, since the entire sampling cone 144 and skimmer cone 145 are heated to a high temperature, the sampling cone 144 and the skimmer cone 145 are cooled by a method such as attaching a cooling block through which cooling water flows inside to the base. It prevents these from melting.

Japanese Unexamined Patent Publication No. 10-40857

The plasma and a part of the sample that have passed through the sampling cone 144 become a supersonic flow and adiabatically expand. Then, it further passes through the hole formed at the top of the skimmer cone 145 and is incident on the second vacuum chamber 142. The size of the hole formed at the top of the sampling cone 144 is, for example, about 1.0 mm in diameter. The diameter of the hole formed at the top of the skimmer cone 145 is, for example, about 0.5 mm. When the sample passes through the hole of the skimmer cone 145, a part of the sample is cooled by the skimmer cone 145 in the vicinity of the hole. As a result, a part of the ionized sample is deionized and precipitated as a solid on the surface of the skimmer cone 145. In particular, when the high-concentration sample is cooled, the amount of precipitation on the surface of the skimmer cone 145 increases in a shorter time. As a result, the hole at the top of the skimmer cone 145 is closed, and the efficiency of introducing ions into the mass spectrometer 130 is significantly reduced. For example, in the case of a sample prepared based on a diluted solution of seawater, a large amount of sodium chloride or magnesium salt is precipitated.

An object to be solved by the present invention is to prevent salt and the like from depositing in the vicinity of the pores formed at the top of the skimmer cone in an inductively coupled plasma mass spectrometer.

The skimmer cone according to the present invention made to solve the above problems is
It is characterized by having a groove formed in the circumferential direction on at least a part of the outer peripheral surface and / and the inner peripheral surface of the conical tip portion.

The skimmer cone according to the present invention is intended to be used in an inductively coupled plasma mass spectrometer. The inductively coupled plasma mass spectrometer includes an ion source having a plasma torch that generates atomic ions from a sample by inductively coupled plasma, and a mass separator that separates and detects the generated atomic ions by mass separation. The ion source is provided in the atmospheric pressure space, and the mass separation portion is provided inside a vacuum chamber having a plurality of vacuum chambers partitioned by a partition wall and the degree of vacuum is gradually increased toward the rear stage side. A sampling cone for forming atomic ions generated by an ion source into a small-diameter ion beam is provided on the inlet side of the vacuum chamber. The skimmer cone according to the present invention is provided on a partition wall located after the sampling cone. The outer peripheral surface of the skimmer cone is irradiated with high-temperature plasma that has passed through the sampling cone. In order to prevent the skimmer cone from melting due to the heat of the high temperature plasma, the skimmer cone is cooled from the base side (partition side) by a cooling block through which cooling water flows. Alternatively, it may be cooled (air-cooled) by the atmosphere outside the vacuum chamber via the partition wall. In either case, the heat applied to the skimmer cone by irradiation with high temperature plasma is transferred to the base side of the skimmer cone.

The skimmer cone according to the present invention is characterized in that grooves are formed in the circumferential direction on the outer peripheral surface and / and the inner peripheral surface thereof. This groove may be formed over the entire circumference in the circumferential direction, or may be partially formed in the circumferential direction. Further, the number of grooves may be one or may be plural.

In the skimmer cone according to the present invention, since the skimmer cone becomes thin at the position of the groove formed on the outer peripheral surface and / and the inner peripheral surface, heat is transferred at the position of the groove when heat is transferred from the tip portion to the base portion. Since the path is narrowed (the cross-sectional area is small), the heat on the tip side (opposite to the partition wall) is less likely to be transferred to the base side than the position where the groove is formed. As a result, the ions generated from the sample are less likely to be cooled in the vicinity of the pores formed at the top of the sampling cone, so that the ions are deionized and salts and the like are precipitated in the vicinity of the pores at the top of the skimmer cone. Can be prevented.

In the skimmer cone according to the present invention, it is preferable that the groove portion is formed on the outer peripheral surface of the skimmer cone. The shape of the groove is not particularly limited, but the cross section of the groove is preferably L-shaped. By forming the groove portion in such a shape, the groove portion can be easily formed by processing using a milling machine or the like.

Further, the inductively coupled plasma mass spectrometer provided with the skimmer cone according to the present invention
a) An ionization unit that ionizes the sample with plasma generated from the raw material gas,
b) A mass separator and its mass that separate the first space maintained at a first pressure lower than atmospheric pressure and the ions generated at the ionization section maintained at a second pressure lower than the first pressure. A vacuum chamber partitioned into a second space in which a detector for detecting ions that have passed through the separation section is housed,
c) A skimmer cone provided on the side of the first space of the partition wall separating the first space and the second space, and at least a part of the outer peripheral surface and / or inside of the conical tip portion. It is characterized by including a skimmer cone having a groove formed in the circumferential direction on the peripheral surface.

By using the skimmer cone according to the present invention in the inductively coupled plasma mass spectrometer, it is possible to prevent salt and the like from precipitating in the vicinity of the pores formed at the top of the skimmer cone.

The block diagram of the main part of an inductively coupled plasma mass spectrometer. FIG. 6 is a block diagram of a main part of an embodiment of an inductively coupled plasma mass spectrometer according to the present invention. An enlarged view of the vicinity of the first vacuum chamber of the inductively coupled plasma mass spectrometer of this embodiment. An enlarged view of a tip portion of an embodiment of a skimmer cone according to the present invention. An enlarged view of the tip of a modified example of the skimmer cone according to the present invention. An enlarged view of the tip of another modified example of the skimmer cone according to the present invention.

An embodiment of the skimmer cone and the inductively coupled plasma mass spectrometer according to the present invention will be described below with reference to the drawings.

FIG. 2 is a configuration diagram of a main part of the inductively coupled plasma mass spectrometer 1 of this embodiment. The inductively coupled plasma mass spectrometer 1 is roughly divided into an ionization unit 10, a mass spectrometer 20, a power supply unit 30, and a control unit 40.

The ionization unit 10 has an ionization chamber 11 which has a substantially atmospheric pressure and is grounded, and a plasma torch 12 is arranged inside the ionization chamber 11. The plasma torch 12 is composed of a sample tube for flowing a liquid sample atomized by nebulizer gas, a plasma gas tube formed on the outer periphery of the sample tube, and a cooling gas tube formed on the outer periphery of the plasma gas tube. There is. Further, an auto sampler 13 for introducing a liquid sample into the sample tube of the plasma torch 12, a nebulizer gas supply source 14 for supplying nebulizer gas to the sample tube, and a plasma gas supply source for supplying plasma gas (argon gas) to the plasma gas tube. 15. A cooling gas supply source (not shown) for supplying cooling gas to the cooling gas pipe is provided.

The mass spectrometer 20 includes a first vacuum chamber 21, a second vacuum chamber 22, and a third vacuum chamber 24 in this order from the side of the plasma torch 12. The first vacuum chamber 21 is an interface with the ionization chamber 11. In the second vacuum chamber 22, an ion lens 221 and a collision cell 222 for converging the flight trajectory of ions are arranged. A quadrupole mass filter 241 (pre-rod 2411 and main rod 2412) and a detector 242 are arranged in the third vacuum chamber 24. In this embodiment, the vacuum chamber is composed of three vacuum chambers, but the number of vacuum chambers to be partitioned can be appropriately changed. The first vacuum chamber 21 of this embodiment corresponds to the first space in the present invention, and the second vacuum chamber 22 and the third vacuum chamber 24 correspond to the second space in the present invention. A sampling cone 211 is provided on the wall surface on the inlet side of the first vacuum chamber 21, and a skimmer cone 224 is provided on the partition wall between the first vacuum chamber 21 and the second vacuum chamber 22. In this embodiment, the mass spectrometer 20 provided with the quadrupole mass filter 241 is used, but a mass separator other than the quadrupole mass filter can also be used. Further, the configuration may include a plurality of mass separation units.

The control unit 40 includes an analysis control unit 42 as a functional block in addition to the storage unit 41. The substance of the control unit 40 is a personal computer, and the analysis control unit 42 is embodied by executing a predetermined program (mass spectrometry program) by the CPU. Further, an input unit 60 such as a keyboard and a mouse and a display unit 70 such as a liquid crystal display are connected to the control unit 40. The data of the output signal from the detector 242 is sequentially stored in the storage unit 41.

When the user instructs the start of analysis through the input unit 60, the autosampler 13 introduces the liquid sample into the sample tube of the plasma torch 12. The liquid sample introduced into the sample tube is atomized by the nebulizer gas (for example, nitrogen gas) supplied from the nebulizer gas supply source 14 and sprayed into the ionization chamber 11. In parallel with this, inductively coupled plasma is generated from the plasma gas (for example, argon gas) supplied from the plasma gas supply source 15. The liquid sample sprayed from the sample tube is atomically ionized by inductively coupled plasma. The high-temperature plasma of 6,000 to 10,000 K generated by the plasma torch 12 of the ionization unit 10 is transmitted along the outer peripheral surface of the sampling cone 211, whereby the entire sampling cone 211 is heated. Further, a part of the plasma passes through the hole at the top of the sampling cone 211 and propagates along the outer peripheral surface of the skimmer cone 224, whereby the entire skimmer cone 224 is heated. As described above, since the sampling cone 211 and the skimmer cone 224 are heated to a high temperature, a cooling mechanism as described later is provided to cool them.

The atomic ions generated by the ionization unit 10 are introduced into the first vacuum chamber 21 in the vacuum chamber through the holes formed at the top of the sampling cone 211. The plasma and a part of the sample that have passed through the sampling cone 211 pass through a hole formed at the top of the skimmer cone 224 while adiabatically expanding as a supersonic flow, and enter the second vacuum chamber 22. When the sample passes through the hole of the skimmer cone 224, the sample passing near the hole is cooled by the skimmer cone 224. The diameter of the hole of the sampling cone 211 is typically about 1.0 mm in diameter. Further, the diameter of the hole of the skimmer cone 224 is smaller than the hole of the sampling cone 211 (that is, typically 1.0 mm or less in diameter), for example, about 0.5 mm in diameter.

FIG. 3 shows a schematic configuration in the vicinity of the first vacuum chamber 21. As described above, a sampling cone 211 is provided at the inlet of the first vacuum chamber 21, and a skimmer cone 224 is provided between the first vacuum chamber 21 and the second vacuum chamber 22. Further, an L-shaped cooling block 212 is attached to the inner surface of the vacuum chamber 20a that houses the mass spectrometer 20. The portion corresponding to the long side of the L-shape is attached to the inner wall surface of the vacuum chamber 20a, and one end thereof (the side opposite to the portion corresponding to the short side) is in contact with the base of the sampling cone 211. Further, the base of the skimmer cone 224 is screwed to the portion corresponding to the short side of the L-shape, and the skimmer cone 224 is removable. A flow path for cooling water is formed inside the cooling block 212, and the sampling cone 211 and the skimmer cone 224 are cooled by the cooling block 212. This prevents the sampling cone 211 and the skimmer cone 224 from being melted by the high-temperature plasma generated by the plasma torch 12. In this embodiment, the sampling cone 211 and the skimmer cone 224 are cooled by the cooling block 212, but the cooling method is arbitrary, and the vacuum chamber 20a is cooled (air-cooled) by the outside air through the partition wall. You can also take it. In either case, the heat applied to the skimmer cone 224 by irradiation with the high temperature plasma is transferred to the base side of the skimmer cone 224. Although the skimmer cone 224 is removable in this embodiment, it may be integrally configured with the partition wall between the first vacuum chamber 21 and the second vacuum chamber 22.

FIG. 4 is an enlarged view of the tip of the skimmer cone 224. As the skimmer cone 224, one made of copper or nickel is used. Further, in order to avoid contamination with impurities in mass spectrometry, a material having a high purity of 99% or more is used. Further, the skimmer cone 224 of the present embodiment includes three groove portions 224a, each of which is formed in the circumferential direction on the outer peripheral surface of the tip portion. Each of the three groove portions 224a is formed over the entire circumferential direction of the skimmer cone, and its cross section is L-shaped with rounded corners. By forming the groove portion 224a in such a shape, the groove portion 224a can be easily formed by processing such as using a milling machine. The convex portion 224b formed between the groove portion 224a of the skimmer cone 224 and the base portion is provided so that the skimmer cone 224 can be attached and detached without touching the tip portion. .. The convex portion 224b is not an essential feature of the present invention, and a skimmer cone 224 without the convex portion 224b may be used.

The skimmer cone 224 of this embodiment is characterized in that a groove portion 224a is formed over the entire peripheral surface of the skimmer cone 224 in the circumferential direction. As a result, the skimmer cone 224 becomes thin at the position of the groove portion 224a, so that when heat is transferred from the tip portion to the base portion, the heat transfer path at the position of the groove portion 224a becomes narrow (the cross-sectional area becomes small). Therefore, the heat on the tip side (opposite to the partition wall) of the position where the groove portion 224a is formed is less likely to be transferred to the base side. Therefore, when the sample passes near the hole of the skimmer cone 224, the sample is less likely to be cooled by the skimmer cone 224. As a result, the ionized sample is less likely to be deionized, so that it is possible to prevent salt and the like from precipitating in the vicinity of the pores at the top of the skimmer cone 224. In the present invention, at least one groove portion 224a formed in the skimmer cone 224 may be formed at a position within 5 mm from the tip end side, and heat may be retained on the tip end side of the groove portion 224a position. preferable.

Conventionally, as described in Patent Document 1, for example, a skimmer cone that is molded so as to gradually become thinner toward the tip and has a sharp cross section (knife edge shape) on the tip side has been used. .. In a skimmer cone having such a shape, by gradually narrowing the heat transfer path toward the tip (reducing the cross-sectional area), it becomes difficult to cool the tip where the hole is formed, so that salt or the like is used. Although there is a possibility that the effect of preventing precipitation can be obtained, since the tip side has a sharp shape, it is easily damaged or deformed when it comes into contact with other parts when cleaning or replacing the skimmer cone. In addition, it is easily deformed by being continuously irradiated with high-temperature plasma. On the other hand, in the skimmer cone 224 of the present embodiment, the thickness of the tip portion can be appropriately adjusted to obtain the required strength, so that damage and deformation can be suppressed.

The above embodiment is an example and can be appropriately modified according to the gist of the present invention. In the above embodiment, three groove portions 224a having an L-shaped cross section are formed on the outer peripheral surface of the skimmer cone 224 over the entire circumference thereof, but the shape and number of the groove portions 224a can be appropriately changed. The skimmer cone according to the present invention is provided with at least one portion where the cross-sectional area becomes smaller (thinner) from the tip portion toward the base portion, and the tip end side (opposite to the partition wall) from the position where the groove portion is formed thereby. It is based on the technical idea of making it difficult for the heat on the side) to be transmitted to the base side, and can be changed as appropriate within that range.

FIG. 5 is an enlarged view of the tip portion of the skimmer cone 225 of the modified example. In the modified example of FIG. 5, a groove portion 225a having an L-shaped cross section is provided on the inner peripheral surface of the tip end portion of the skimmer cone 225 as in the above embodiment. Further, FIG. 6 is an enlarged view of the tip portion of the skimmer cone 226 of another modified example. In the modified example of FIG. 6, the groove portions 226a and 226b are partially formed in the circumferential direction on both the inner peripheral surface and the outer peripheral surface of the skimmer cone 226. The same effect as that of the above embodiment can also be obtained by using the skimmer cones 225 and 226 of the modified examples as shown in FIGS. 4 and 5. As the groove, in addition to the above-mentioned ones, various ones such as those having a V-shaped cross section and those having a semicircular cross section can be used.

1 ... Inductively coupled plasma mass spectrometer 10 ... Ionization unit 11 ... Ionization chamber 12 ... Plasma torch 13 ... Auto sampler 14 ... Nebulizer gas supply source 15 ... Plasma gas supply source 20 ... Mass spectrometer 20a ... Vacuum chamber 21 ... First vacuum Chamber 211 ... Sampling cone 212 ... Cooling block 22 ... Second vacuum chamber 221 ... Ion lens 222 ... Collision cell 223 ... Energy barrier forming electrode 224, 225, 226 ... Skimmer cone 224a, 225a, 226a ... Groove 24 ... Third vacuum chamber 241 ... Quadrupole mass filter 2411 ... Pre-rod 2412 ... Main rod 242 ... Detector 30 ... Power supply unit 40 ... Control unit 41 ... Storage unit 42 ... Analysis control unit 60 ... Input unit 70 ... Display unit

Claims (8)

A skimmer cone characterized by having a groove formed in the circumferential direction on at least a part of the outer peripheral surface and / and the inner peripheral surface of a conical tip portion. The skimmer cone according to claim 1, which is made of nickel or copper having a purity of 99% or more. The skimmer cone according to claim 1, wherein the diameter of the hole formed in the tip portion is 1.0 mm or less. The skimmer cone according to claim 1, wherein the groove is formed on the outer peripheral side of the skimmer cone. The skimmer cone according to claim 1, wherein the cross section of the groove portion is L-shaped. The skimmer cone according to claim 1, wherein the groove is formed at a position within 5 mm from the tip. The skimmer cone according to claim 1, wherein a plurality of the grooves are formed. a) An ionization unit that ionizes the sample with plasma generated from the raw material gas,
b) A mass separator and its mass that separate the first space maintained at a first pressure lower than atmospheric pressure and the ions generated at the ionization section maintained at a second pressure lower than the first pressure. A vacuum chamber partitioned into a second space in which a detector for detecting ions that have passed through the separation section is housed,
c) A skimmer cone provided on the side of the first space of the partition partition separating the first space and the second space, and at least a part of the outer peripheral surface and / or inside of the conical tip portion. An inductively coupled plasma mass spectrometer characterized by including a skimmer cone having a groove formed in the circumferential direction on the peripheral surface.

Images